Best way to get a region setup for complex geometry.

Hello,

I work in the cement industry and I am trying to model the particle flow of the material in the preheat that we have to determine the optimal particle distribution and cyclone efficiency. I have managed to do this in OpenFOAM-dev with the new MPPIC solver. However I would like to see the difference between LIGGGHTS and the MPPIC solver. From the best of my understanding LIGGGHTS should produce a more accurate result.

The geometry is complete so a box won't be able to work for the region.

Now there seems to be two ways that I think I can go about creating the region however I can not find a tutorial that shows me how it is done.

One I is creating multiple boundaries with multiple region boxes and build like lego blocks for the boundaries. Is this possible and how would one do it?

Another would be using the mesh/tet function

The geometry that I used was modeled in blender then meshed with snappyHexMesh, so it can be tetrahedralize in paraview and exported as a vtk mesh or I can use foamToVTK and get the VTK mesh out. will this work?

I was thinking of using the cyclone tutorial in openFOAM to start with to test mesh/tet out. Has anyone done this before?
Can I use the mesh/tet as the region and cyclone.stl as the wall, even though they lie on top of each other? Should I scale up the mesh/tet a little to be slightly bigger than the stl?

I do know that the cyclone tutorial will fit into a box so it is easier to get running than my actual case. but I want to get it running with the boundary the same as the internal mesh that openFoam uses.

Thanks.